1. Field of the Invention
The present invention relates to a high definition television (HDTV) for displaying images contained in broadcasting signals of mutually different broadcasting systems, and more particularly, to an HDTV for displaying images contained in a digital broadcasting signal of an HDTV system and an analog broadcasting signal of a PAL (Phase Alternation by Line) system or an NTSC (National Television System Committee) system.
2. Description of the Related Art
As is well known, a frame format of a digital broadcasting signal according to an HDTV system is considerably different from that of an analog broadcasting signal of an NTSC system or a PAL system. A frame format refers to a vertical frequency which is the number of frames per second of an image signal contained in a broadcasting signal, a horizontal frequency which is the number of horizontal lines per second of an image signal contained in a broadcasting signal, and an aspect ratio of an image to be displayed. In the frame format, the horizontal frequency and the aspect ratio of an image signal contained in the high definition (HD) digital broadcasting signal are 31.50 KHz and 16:9, respectively. Meanwhile, in the case of an image signal contained in the NTSC analog broadcasting signal, the horizontal frequency and the aspect ratio are 15.75 KHz and 4:3, respectively. Also, in a digital broadcasting signal according to the HDTV system, the frame format differs slightly according to the HDTV system specified in each country.
Due to the above differences, the HDTV for displaying the image signal contained in the conventional HD digital broadcasting signal or the NTSC analog broadcasting signal comprises an HD digital broadcasting signal processor for restoring a first image signal which is an image signal contained in the HD digital broadcasting signal, an NTSC analog broadcasting signal processor for restoring a second image signal which is an image signal contained in the NTSC analog broadcasting signal, two format converters, and a switch for selectively outputting only one image signal among the first and second image signals according to a user command. One of the two format converters is a first format converter for converting a frame format of the first image signal into a frame format of the HDTV system set during manufacturing, and the other is a second format converter for converting a frame format of the second image signal contained in the NTSC analog broadcasting signal into a frame format which is the same as that of the first image signal whose format has been converted by the first format converter. However, since such a conventional HDTV selectively outputs only one of a plurality of image signals contained in the broadcasting signals of mutually different broadcasting systems, the HDTV cannot simultaneously display on a screen a plurality of images whose broadcasting systems differ from each other.
To solve the above problems, it is an object of the present invention to provide an HDTV for synthesizing a plurality of image signals contained in the broadcasting signals of mutually different broadcasting systems into a single picture-in-picture (PIP) image signal and displaying the synthesized PIP image signal on a screen, using an image signal synthesizer comprising two memories for storing a respectively format-converted image signal and a timing signal generator for time-base-compressing each image signal stored in the two memories and generating a timing signal for alternately outputting each stored image signal.
To accomplish the above object of the present invention, there is provided an HDTV for displaying images contained in an HD digital broadcasting signal and an analog broadcasting signal input via an antenna or an external input port on a screen, the HDTV comprising: a first broadcasting signal processor for restoring a first image signal which is an image signal contained in the HD digital broadcasting signal; a second broadcasting signal processor for restoring a second image signal which is an image signal contained in the analog broadcasting signal; a host computer; a first format converter for converting the frame format of the first image signal restored by the first broadcasting signal processor into a predetermined frame format under the control of the host computer; a second format converter for converting the frame format of the second image signal restored by the second broadcasting signal processor into the predetermined frame format; an image signal synthesizer for synthesizing the first and second image signals format-converted by the first and second format converters into a single PIP image signal; and a display module for visually displaying the PIP image signal on the screen.